1. Field of the Invention
The invention in general relates to underwater transducers, and particularly to a hydrophone which is shaded to improve its performance.
2. Description of the Prior Art
A hydrophone is a transducer having a certain beam pattern used in the underwater environment alone, or with other transducers of an array, to detect targets. In order to improve the beam pattern, use is made of amplitude shading. Thus, by applying different weighting functions to the segments of a transducer or to the transducers of an array, the side lobe level of the beam pattern may be controlled.
Amplitude shading is also used in conjunction with a hydrophone or a hydrophone array mounted on a carrier for movement through the water by using the array aperture to discriminate against flow noise by a well-known technique known as wave vector filtering. The hydrophone transducer is made up of a plurality of transducer sections having small gaps between sections, the output of each section being weighted in accordance with any well-known shading function, and then combined to provide a hydrophone output signal. This technique requires a multitude of preamplifiers and the breaks or gaps between transducer segments can result in spurious or aliasing frequencies indicating a target where in actuality no target exists.
In the case of a stationary hydrophone, grating lobes in the beam pattern may be introduced, causing certain higher than desired side lobe levels.
The transducer of the present invention obviates the objectionable consequences of the prior art type of shading.